Over the last few years, how and when to provide tepid water to emergency eyewash and shower equipment has become a more important part of designing plumbing systems to serve these fixtures. Although tepid water has been a requirement of ANSI Z358.1 since 1998, no specific parameters were suggested until the 2004 version was released.

Tepid water is defined by ANSI Z358.1-2004 as "moderately warm, lukewarm," but the standard does not stipulate a temperature. Guidelines to follow in order to meet the requirement are found in Appendix B6. Here it states that "temperatures greater than 100° F have been proven to be harmful to the eyes and may enhance chemical interaction with the eyes or skin." This, in effect, provides an upper limit. ANSI goes on to say that "60° F should be a suitable lower parameter for tepid flushing fluid without causing hypothermia," which provides a lower limit.

The wild card in this process is that different chemicals react differently with water at different temperatures, which is why the tepid temperature standard must remain somewhat vague. The temperature range is meant to accommodate all different types of applications; therefore it is recommended that a medical advisor be consulted to determine exactly what temperature of water is best for each application.

Abundant flushing of the eyes and/or body after an accident is crucial. As with most Material Safety Data Sheets provided for hazardous chemicals, ANSI suggests that a user needs to be able to flush/drench the eyes or body for a full 15 minutes. This is why water temperature is so important. Cold water from a city supply may prohibit an individual from remaining under the shower or eyewash for the full 15 minutes, which can cause further damage to the eyes or skin.

The most common solution for providing tepid water is to incorporate a thermostatic mixing valve into your plumbing system. TMVs are designed to mix a hot and cold water supply to provide a steady flow of water at a constant temperature. Most TMVs are factory set at 85° F, but can be adjusted depending on the specific temperature requirements of the hazard.

It is important to use TMVs designed specifically for emergency fixtures. These valves are built to include a cold water bypass, which allows cold water to pass through the valve in the event of hot water interruption, but will shut the valve down completely upon a cold water failure.

Another solution for areas where a dedicated hot water supply is unavailable is a packaged, turnkey, skid-mounted tempering system. These systems typically include a water heater, expansion tank, TMV and recirculation pump to provide a recirculating loop of tepid water that can be run to multiple emergency fixtures throughout a facility.

By supplying tepid water through such a loop, you can eliminate TMVs at every fixture and eliminate the need to run dedicated hot and cold water lines to each emergency fixture, which can save substantially on construction costs.

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